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Lecture notes on Thermodynamics
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First Law Closed System Formulas
ISOMETRIC (Isochoric) PROCESS
a.) Relationship between P and T.
T1/T2 = P1/P2
b.) Non-flow work.
Wn =
c.) The change of internal energy
U = mcv(T2 T1)
d.) The heat transferred
Q = mcv(T2 T1)
e.) The change of enthalpy
H = mcp(T2 - T1)
f.) Irreversible non-flow constant volume process
Q = U + Wn
where: For reversible non-flow, Wn = 0
For irreversible nonflow, Wn 0
Wn = non-flow work
ISOBARIC PROCESS
a) Relationship between V and T
T1/T2 = V1/V2
b) Nonflow work
Wn = = P(V2 V1) = mR(T2 T1)
c) Change of internal energy
U = mcv (T2 T1)
d) Heat transferred
Q = mcp (T2 T1)
e) Change of enthalpy
H = mcp (T2 T1)
ISOTHERMAL PROCESS
(a.) Relationship between P and V
P1V1 = P2V2
(b.) Nonflow work
Wn = P1V1lnV2/V1 = mRT1lnV2/V1
(c.) The change of internal energy
U = O
(d.) The heat transferred
Q = Wn = P1V1lnV2/V1 = mRT1lnP1/P2
(e.) The change of enthalpy
H = 0
ISENTROPIC PROCESS
1. Relationship among P, V and T.
(a) Relationship between P and V
P1V1k = P2V2k = C
(b) Relation between T and V
From P1 V1k = P2 V2k and P1V1/T1 = P2V2/T2, we have
T2/T1 = [V1/V2]k-1
(c ) Relation between T and P
T2/T1 = [p2/p1](k-1)/k
2. Nonflow work.
From PVk = C, P = CV-k
Wn = PdV = C-kdV = C V-kdV
Integrating and simplifying
Wn = P2V2 P1V1 / (1- k) = mR(T2 T1) / (1 k)
3. The change of internal energy.
U = mCv (T2 T1)
4. The heat transferred.
Q = 0
5. The change of enthalpy.
H = mCp (T2 T1)
6. The change of entropy.
S = 0
POLYTROPIC PROCESS
1. Relationship among p, V, and T
(a) Relation between P and V
P1V1n = P2V2n
(b) Relation between T and V
T2/T1 = [V1/V2]n-1
(c) Relation between T and p
T2/T1 = [p2/p1](n-1)/n
2. Nonflow work
Wn = pdV = P2V2 P1V1 / 1-n = mR(T2-T1) / 1-n
3. The change of internal energy.
U = mCv(T2 T1)
4. The heat transferred. Q = U + Wn
= mcv (T2 T1) + mR (T2 T1)/(1 - n)
= m [(cv ncv + R)/(1 n)] (T2 T1)
= m [(cp ncv)/(1 n)] (T2 T1)
= mcv [(k n)/(1 n)] (T2 T1)
Q = mCn(T2 T1)
Cn = Cv [(k n)/(1 n)], the polytropic specific heat
5. The change of enthalpy
H = mCp (T2 T1)
First Law Open System Formulas
Mass:
Energy:
Nozzle/Diffuser:
2 2
1 21 20
2
V Vh h
Turbine and Compressor:
Heat Exchangers:
2 2
2 2
i ei i i e e e
i e
V Vm h gz m h gz
Throttling Device:
i eh h
Transient System
Mass:
Energy:
cvi e
i e
dmm m
dt
2 2
2 2
cv i ecv cv i i i e e e
i e
dE V VQ W m h gz m h gz
dt
2 2
1 21 2 1 2
2
W V Vh h g z z
m
0cv cv i ei e
m t m m m
0 0
0t t
cv cv cv cv i i e e
i e
U t U Q W m hdt m h dt